This invention relates generally to outboard marine engines and more particularly to a transmission drain plug which is transparent in order to provide a quick visual indication of whether and to what extent water has seeped into the submersible transmission case of an outboard engine.
In outboard marine engines, the transmission is contained in a lower unit which is submerged in normal use. Consequently, even though the submersible transmission case is equipped with various types of gaskets and other seals, water can at times leak past the seals and seep into the transmission case. If water seeps into the transmission to any significant extent, it can severely impair the lubricating ability of the transmission oil. As a result of this contamination of the oil by water seepage, the gears, bearings, shaft and other parts of the drive line can be damaged or destroyed, often necessitating costly and time consuming repairs.
The lower unit of an outboard engine normally includes two plugged openings. One opening is located on top of the transmission and is used to add oil to the transmission case, and the other opening is located at the bottom of the transmission and is used for the drainage of oil. At present, the only method of determining whether water has seeped into the transmission involves draining oil from the drain opening so that it can be visually inspected for the presence of water. It is then necessary to replenish the oil through the fill opening.
At least in part because of the time and difficulty involved in carrying out this inspection procedure, most boat owners check the oil condition no more often than once a year, usually when the engine is being prepared for winter storage or inspected to determine if damage has occurred during the boating season. Annual inspection too infrequent to reliably detect the presence of water before it can cause damage. As a consequence, the transmissions of many outboard engines become damaged by water seepage before the problem is discovered.
The present invention meets a long felt need in the outboard marine industry in that it provides a quick and easy way for the owners and operators of outboard engines to determine whether water has seeped into the submersible lower unit which includes the transmission. In accordance with the invention, the normal drain plug of the transmission case is removed and replaced by a special plug which serves both to plug the drain opening and to provide an easily visible indication of the condition of the lubricating oil in the transmission. The plug is transparent so that the transmission oil can be sighted through it and its color indicates the water content, if any. If the transparent plug indicates a blue, black or green color, the oil condition is good and water seepage has not occurred. If the plug indicates yellow or amber, some water has leaked into the transmission and mixed with the oil. A clear indication means that fairly large quantities of water have seeped into the transmission case and it is necessary to take immediate corrective measures in order to avoid damage.
Although transparent plugs and various types of sight glasses have been employed in the past in connection with checking various engine fluids, to my knowledge transparent plugs have not been used on the submersible transmission case of an outboard marine engine. It is a particularly important feature of the invention that the transparent plug has a special configuration that creates magnification in order to enhance the visibility of the transmission case interior. The tip of the plug and the outer surface of its head are both convex surfaces which provide a lens effect. A specially shaped cavity in the plug enhances the lens effect to provide enough magnification that the oil condition can be easily observed from a distance of 8-10 feet. As a result, water that seeps into the transmission case can be detected at an early enough stage to prevent damage to the components of the transmission.